Method of reporting system information in a wireless communication system and device for supporting same

ABSTRACT

The present invention relates to a method for a terminal to report system information in a wireless communication system. The method includes: transmitting a previously-obtained system information availability indicator that indicates to a serving cell that there is previously obtained system information on a neighboring cell; and receiving a system report request from the serving cell; and transmitting a system information report to the serving cell in response to the system report request. The system report request includes a previously obtained system information report request indicator. When the previously obtained system information report request indicator indicates that there is a report on the previously obtained system information, the system information report includes the previously obtained system information and the previously obtained system information is system information obtained from the neighboring cell before the system report request is received.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2012/005582, filed on Jul. 13, 2012,which claims the benefit of U.S. Provisional Application Ser. No.61/507,606, filed on Jul. 14, 2011, the contents of which are all herebyincorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system and,more particularly, to a method of reporting, by user equipment, systeminformation in a wireless communication system and an apparatus forsupporting the same.

2. Related Art

3^(rd) generation partnership project (3GPP) long term evolution (LTE)which is improvement of a universal mobile telecommunications system(UMTS) is introduced as 3GPP release 8. The 3GPP LTE uses orthogonalfrequency division multiple access (OFDMA) in a downlink and uses singlecarrier-frequency division multiple access (SC-FDMA) in an uplink.Multiple input multiple output (MIMO) having maximum four antennas areadopted. In recent years, 3GPP LTE-advanced (LTE-A) which is anevolution of the 3GPP LTE has been discussed.

A closed subscriber group (CSG) allows a limited access for only aspecific subscriber to be introduced to provide a service having higherquality. A base station that can provide a CSG service may be homeeNodeB (HNB) and a cell providing an authorized service to CSGsubscribers may be a CSG cell. In the 3GPP, a basic requirement of theCSG is disclosed in 3GPP TS 22.220 V1.0.1 (2008-12) “Servicerequirements for Home NodeBs and Home eNodeBs (Release 9)”.

A feature of a CSG cell restrictedly providing the service isillustrated even in handover to the CSG cell. Whether a user equipment(UE) is a CSG member of a corresponding cell may be problematic inperforming the handover to the CSG cell. As a result, the handover tothe CSG cell may be implemented by a first step in which the UE reportsa cell measurement result and a second step in which the UE acquiressystem information from a target cell and reports the acquired systeminformation to a service cell.

When a message that instructs UE to report system information about aneighboring cell is received from a serving cell, the UE accesses theneighboring cell and obtains the system information. The UE sends theobtained system information to the serving cell. While the UE accessesthe neighboring cell in order to obtain the system information, theserving cell is unable to send any command/message/data to the UE.

Meanwhile, the UE may obtain the system information about theneighboring cell before being instructed by the serving cell to reportthe system information. Even in such a case, a step of leaving, by theUE, the serving cell and accessing the neighboring cell in order tonewly obtain the system information about the neighboring cell may beunnecessary, if necessary. Accordingly, there is a need for a moreefficient method of reporting, by UE, system information.

SUMMARY OF THE INVENTION

A technical problem to be solved by the present invention is to providea report method performed by UE in a wireless communication system andan apparatus for supporting the same.

In an aspect, a method of reporting, by user equipment, systeminformation in a wireless communication system is provided. The methodincludes transmitting a ready-acquired system information availabilityindicator, notifying a serving cell that ready-acquired systeminformation about a neighboring cell is present, to the serving cell,receiving a system information reporting request from the serving cell,and sending a system information report to the serving cell in responseto the system reporting request. If the system reporting requestcomprises a ready-acquired system information reporting requestindicator and the ready-acquired system information reporting requestindicator indicates that the ready-acquired system information is to bereported, the system information report includes the ready-acquiredsystem information. The ready-acquired system information is systeminformation acquired from the neighboring cell before receiving thesystem reporting request.

The method of claim may further include, if the system reporting requestcomprises the ready-acquired system information reporting requestindicator and the ready-acquired system information reporting requestindicator indicates that the system information is to be acquired fromthe neighboring cell and to be reported, acquiring new systeminformation from the neighboring cell and reporting the newly acquiredsystem information to the serving cell.

The method may further include, if the system reporting request does notinclude the ready-acquired system information reporting requestindicator, acquiring the new system information from the neighboringcell and reporting the new acquired system information to the servingcell.

The system information report may further include an indicatorindicating whether system information included in the system informationreport is the ready-acquired system information or the newly acquiredsystem information.

The method may further include receiving a ready-acquired systeminformation query indicator from the serving cell. The ready-acquiredsystem information query indicator may request to notify that whetherthe ready-acquired system information is present. The ready-acquiredsystem information availability indicator may be transmitted in responseto the ready-acquired system information query indicator.

The method may further include transmitting control information aboutthe ready-acquired system information along with the ready-acquiredsystem information availability indicator.

The control information comprises information about an identifier of theneighboring cell related to the ready-acquired system information,indication information indicating a point of time at which theready-acquired system information was acquired, and informationindicating a type of ready-acquired system information.

The ready-acquired system information query indicator may be included ina measurement configuration message and transmitted. The ready-acquiredsystem information availability indicator may be included in ameasurement report message and transmitted.

In another aspect, user equipment operating in a wireless communicationsystem is provided. The user equipment includes a Radio Frequency (RF)unit sending and receiving radio signals, and a processor functionallyconnected to the RF unit. The processor is configured for transmitting aready-acquired system information availability indicator, notifying aserving cell that ready-acquired system information about a neighboringcell is present, to the serving cell, receiving a system informationreporting request from the serving cell, and sending a systeminformation report to the serving cell in response to the systemreporting request. If the system reporting request comprises aready-acquired system information reporting request indicator and theready-acquired system information reporting request indicator indicatesthat the ready-acquired system information is to be reported, the systeminformation report includes the ready-acquired system information. Theready-acquired system information is system information acquired fromthe neighboring cell before receiving the system reporting request.

Through the method of reporting system information in accordance with anembodiment of the present invention, UE can effectively notify a servingcell that it has system information about a neighboring cell.Accordingly, the serving cell can request a report on system informationabout a neighboring cell from the UE in an optimized way. As a result,the time that is consumed for the serving cell to obtain systeminformation about a neighboring cell can be reduced. If such a method ofreporting system information is applied to a mobility performing methodof UE, such as a handover, delay occurring when mobility is performedcan be reduced and mobility can be performed more efficiently. This canlead to the improvement of communication quality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless communication system according to thepresent invention.

FIG. 2 is a block diagram illustrating a radio protocol architecture fora user plane.

FIG. 3 is a block diagram illustrating a radio protocol architecture fora control plane.

FIG. 4 is a flowchart illustrating an operation of a UE in an RRC idlestate.

FIG. 5 is a flowchart illustrating a process of establishing an RRCconnection.

FIG. 6 is a flowchart illustrating a process of reconfiguring the RRCconnection.

FIG. 7 is an exemplary diagram illustrating a radio link failure.

FIG. 8 is a flowchart illustrating a success in a process ofreestablishing a connection.

FIG. 9 is a flowchart illustrating a failure in the process ofreestablishing the connection.

FIG. 10 is a flowchart illustrating the existing measurement performingmethod.

FIG. 11 illustrates one example of a measurement configurationconfigured for the UE.

FIG. 12 illustrates an example of deleting a measurement identity.

FIG. 13 illustrates an example of deleting a measurement object.

FIG. 14 is a diagram illustrating one example of a wirelesscommunication system illustrating a HeNB operation.

FIG. 15 exemplifies a CSG scenario.

FIG. 16 exemplifies a pico scenario.

FIG. 17 is a flowchart illustrating a method of reporting systeminformation in accordance with an embodiment of the present invention.

FIG. 18 is a block diagram showing a wireless device in which anembodiment of the present invention can be implemented.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 illustrates a wireless communication system according to thepresent invention. The wireless communication system may also be calledan evolved-UMTS terrestrial radio access network (E-UTRAN) or a longterm evolution (LTE)/LTE-A system.

The E-UTRAN includes a base station (BS) 20 that provides a controlplane and a user plane to a user equipment (UE) 10. The UE 10 may befixed or movable and may be called other terms such as a mobile station(MS), a user terminal (UT), a subscriber station (SS), a mobile terminal(MT), a wireless device, and the like. The base station 20 represents afixed station that communicates with the UE 10, and may be called otherterms such as an evolved-NodeB (eNB), a base transceiver system (BTS),an access point, and the like.

The base stations 20 may be connected to each other through an X2interface. The base station 20 is connected with an evolved packet core(EPC) 30 through an S1 interface, in more detail, a mobility managemententity (MME) through an S1 MME and a serving gateway (S-GW) through anSI-U.

The EPC 30 is constituted the MME, the S-GW, and a packet data networkgateway (P-GW). The MME has access information of the UE or informationon a capability of the UE, and the information is primarily used formobility management of the UE. The S-GW is a gateway having the E-UTRANas an end point and the P-GW is a gateway having a PDN as the end point.

Layers of a radio interface protocol between the UE and a network may bedivided into an L1 (first layer), an L2 (second layer), and an L3 (thirdlayer) based three lower layers of an open system interconnection (OSI)reference model which is widely known in a communication system andamong them, a physical layer that belongs to the first layer provides aninformation transfer service using a physical channel and a radioresource control (RRC) layer positioned on the third layer serves tocontrol radio resources between the UE and the network. To this end, theRRC layer exchanges an RRC message between the UE and the base station.

FIG. 2 is a block diagram illustrating a radio protocol architecture fora user plane. FIG. 3 is a block diagram illustrating a radio protocolarchitecture for a control plane. A data plane is a protocol stack foruser data transmission and the control plane is a protocol stack fortransmitting a control signal.

Referring to FIGS. 2 and 3, a physical (PHY) layer provides theinformation transfer service to an upper layer by using the physicalchannel. The physical layer is connected with a medium access control(MAC) layer as an upper layer through a transport channel. Data movebetween the MAC layer and the physical layer through the transportchannel. The transport channel is classified depending on a transmissionmethod and a transmission feature through a radio interface.

Data move between different physical layers, that is, between physicallayers of a transmitter and a receiver through the physical channel. Thephysical channel may be modulated by orthogonal frequency divisionmultiplexing (OFDM) and uses a time and a frequency as the radioresource.

A function of the MAC layer includes mapping between a logic channel andthe transport channel, and multiplexing/demultiplexing to a transportblock provided to the physical channel onto the transport channel of anMAC service data unit (SDU) that belongs to the logic channel. The MAClayer provides a service to a radio link control (RLC) layer through thelogic channel.

A function of the RLC layer includes concatenation, segmentation, andreassembly of an RLC SDU. In order to assure various quality of services(QoS) requested by a radio bearer (RB), the RLC layer provides threeoperating modes of a transparent mode (TM), an unacknowledged mode (UM),and an acknowledged mode (AM). An AM RLC provides error correctionthrough an automatic repeat request (ARQ).

A function of a packet data convergence protocol (PDCP) layer on theuser plane includes transferring of user data, header compression, andciphering. A function of a packet data convergence protocol (PDCP) layeron the user plane includes transferring of control plane data andciphering/integrity protection.

The radio resource control (RRC) layer is defined only on the controlplane. The RRC layer serves to control the logic channel, the transportchannel and the physical channels in association with configuration,re-configuration, and release of radio bearers. The RB means a logicroute provided by the first layer (PHY layer) and the second layers (theMAC layer, the RLC layer, and the PDCP layer) in order to transfer databetween the UE and the network.

Setting the RB defines features of the radio protocol layer and channelin order to provide a specific service and means a process of settingrespective detailed parameters and operating methods. The RB may bere-divided into two types of a signaling RB (SRB) and a data RB (DRB).The SRB is used as a passage for transmitting the RRC message on thecontrol plane and the DRB is used as a passage for transmitting the userdata on the user plane.

When an RRC connection is established between the RRC layer of the UEand the RRC layer of the E-UTRAN, the UE is in an RRC connected stateand if not, the UE is in an RRC idle state.

A downlink transport channel for transmitting data from the network tothe UE includes a broadcast channel (BCH) for transmitting systeminformation and besides, the downlink transport channel includes adownlink shared channel (SCH) for transmitting user traffic or a controlmessage. Traffic or a control message of a downlink multicast orbroadcast service may be transported through the downlink SCH ortransported through an additional downlink multicast channel (MCH).Meanwhile, an uplink transport channel for transporting data from the UEto the network includes a random access channel (RACH) for transportingan initial control message and besides, an uplink shared channel (SCH)for transporting the user traffic or control message.

The logical channel that is positioned on the transport channel andmapped to the transport channel includes a broadcast control channel(BCCH), a paging control channel (PCCH), a common control channel(CCCH), a multicast control channel (MCCH), a multicast traffic channel(MTCH), and the like.

The physical channel is constituted by a plurality of OFDM symbols in atime domain and a plurality of sub-carriers in a frequency domain. Onesub-frame is constituted by the plurality of OFDM symbols in the timedomain. A resource block as a resource allocation unit is constituted bythe plurality of OFDM symbols and the plurality of sub-carriers.Further, each sub-frame may use specific sub-carriers of specific OFDMsymbols (e.g., a first OFDM symbol) of a corresponding sub-frame for thephysical downlink control channel (PDCCH), that is, an L1/L2 controlchannel. A transmission time interval (TTI) is a unit time oftransmitting the sub-frame.

Hereinafter, the RRC state and the RRC connection method of the UE willbe described in detail.

The RRC state represents whether the RRC layer of the UE is logicallyconnected with the RRC layer of the E-UTRAN and a case in which both RRClayers are logically connected to each other is called the RRCconnection state and a case in which both RRC layers are not logicallyconnected to each other is called the RRC idle state. Since the RRCconnection exists in the UE in the RRC connection state, the E-UTRAN maydetermine the existence of the corresponding UE by the unit of a cell tothereby effectively control the UE. On the contrary, the E-UTRAN may notdetermine the UE in the RRC idle state and a core network (CN) ismanaged by the unit of a tracking area which a region unit larger thanthe cell. That is, it is determined whether the UE in the RRC idle stateexists by the unit of a large region, and the UE needs to move to theRRC connection state in order to receive a general mobile communicationservice such as voice or data.

When a user first turns on a power supply of the UE, the UE firstretrieves an appropriate and thereafter, the UE stays in the RRC idlestate in the corresponding cell. The UE in the RRC idle stateestablishes the RRC connection with the E-UTRAN through an RRCconnection procedure at least when the UE in the RRC idle state needs tomake the RRC connection, and is transited to the RRC connections state.Cases in which the UE in the RRC idle state needs to make the RRCconnection are various, and for example, uplink data transmission isrequired due to a user's call attempt or when a paging message isreceived from the E-UTRAN, the cases may include response messagetransmission thereto.

A non-access stratum layer located above the RRC layer performsfunctions such as session management and mobility management.

In order to manage mobility of the UE on the NAS layer, two states ofEPS mobility management (EMM)-REGISTERED and EMM-DEREGISTERED aredefined and both states are applied to the UE and the MME. An initial UEis in the EMM-DEREGISTERED state and the UE performs a process ofregistering the initial UE in a corresponding network through an initialattach procedure in order to access the network. When the attachprocedure is successfully performed, the UE and the MME are in theEMM-REGISTERED state.

In order to manage a signaling connection between the UE and the EPC,two states of an EPS connection management (ECM)-IDLE state and anECM-CONNECTED state are defined and both states are applied to the UEand the MME. When the UE in the ECM-IDLE state makes the RRC connectionwith the E-UTRAN, the corresponding UE is in the ECM-CONNECTED state.When the MME in the ECM-IDLE state makes an S1 connection with theE-UTRAN, the MME is in the ECM-CONNECTED state. When the UE is in theECM-IDLE state, the E-UTRAN does not have context information of the UE.Therefore, the UE in the ECM-IDLE state performs a UE based mobilityassociated procedure such as cell selection or cell reselection withoutthe need for receiving a command of the network. On the contrary, whenthe UE is in the ECM-CONNECTED state, the mobility of the UE is managedby the command of the network. When the position of the UE in theECM-IDLE state is different from a position which the network knows, theUE notifies a corresponding position of the UE to the network through atracking area update procedure.

Next, the system information will be described.

The system information includes required information which the UE needsto know to access the base station. Therefore, the UE needs to receiveall of the system information before accessing the base station andfurther, the UE continuously needs to have latest system information. Inaddition, since the system information is information which all UEs inone cell need to know, the base station periodically transmits thesystem information.

According to Phrase 5.2.2 of 3GPP TS 36.331 V8.7.0 (2009-09) “RadioResource Control (RRC); Protocol specification (Release 8)”, the systeminformation is divided in to a master information block (MIB), ascheduling block (SB), and a system information block (SIB). The MIBallows the UE to know a physical component, for example, a bandwidth.The SB allows the UE to know transmission information of the SIBs, forexample, a transmission period, and the like. The SIB is an aggregate ofassociated system information. For example, any SIB includes onlyinformation on a neighboring cell and any SIB includes only informationon a uplink wireless channel used by the UE.

In general, a service which the network provides to the UE may bedivided into three types. Further, the UE differently recognizes even atype of the cell by considering which service the UE receives. Theservice type will be first described below and thereafter, the type ofthe cell will be described.

1) Limited service: The service may provide an emergency call and anearthquake and Tsunami warning system (ETWS), and provide the emergencycall and the earthquake and Tsunami warning system (ETWS) in anacceptable cell.

2) Normal service: The service may mean a public use general service andmay provide the public use general service in a suitable or normal cell.

3) Operator service: The service may mean a service for a communicationnetwork operator and only the communication network operator may use thecell and a general user may not use the cell.

The type of the cell may be divided as below in association with theservice type provided by the cell.

1) Acceptable cell: Cell where the UE may receive the limited service.The cell is a cell that is not barred in terms of the corresponding UEand satisfies a cell selection criterion of the UE.

2) Suitable cell: Cell where the UE may receive the suitable service.The cell satisfies a condition of the acceptable cell andsimultaneously, satisfies additional conditions. As the additionalconditions, the cell needs to belong to a public land mobile network(PLMN) which the corresponding UE may access and needs to be a cellwhere execution of the tracking area update procedure of the UE is notbarred. When the corresponding cell is the CSG cell, the correspondingcell needs to be a cell where the UE may access the cell as a CSGmember.

3) Barred cell: The cell is a cell where information indicating that thecorresponding cell is a cell barred through the system information isbroadcasted.

4) Reserved cell: The cell is a cell where information indicating thatthe corresponding cell is a cell reserved through the system informationis broadcasted.

FIG. 4 is a flowchart illustrating an operation of a UE in an RRC idlestate. FIG. 4 illustrates a procedure of registering a UE of whichinitial power is turned on in the network through a cell selectionprocess and thereafter, cell reselection is performed as necessary.

Referring to FIG. 4, the UE selects radio access technology (RAT) forcommunicating with the public land mobile network from which the UEitself intends to receive the service (S410). Information on the PLMNand the RAT may be selected by a user of the UE and the informationstored in a universal subscriber identity module (USIM) may be used.

The UE selects a cell having a largest value among cell having measuredlarger signal intensity or quality than specific values (cell selection)(S420). The UE of which power is turned on performs the cell selectionand the execution of the cell selection may be called initial cellselection. A cell selection procedure will be described below in detail.After the cell selection, the UE receives the system information whichthe base station periodically sends. The aforementioned specific valuerepresents a value defined in the system in order to receive anassurance for quality of a physical signal in transmitting/receivingdata. Therefore, the value may vary depending on the applied RAT.

When network registration is required, the UE performs a networkregistration procedure (S430). The UE registers its own information(e.g., IMSI) in order to receive a service (e.g., paging)n from thenetwork. The UE does not register the information in the accessednetwork whenever selecting the cell, and registers the information wheninformation (e.g., a tracking area identity (TAI) of the network thatreceives from the system information) is different from information on anetwork known by the UE).

The UE performs the cell reselection based on a service environmentprovided by the cell or an environment of the UE (S440). When a value ofmeasured intensity or quality of the signal from a base station fromwhich the UE receives the service is smaller than a value measured froma base station of a neighboring cell, the UE selects one of other cellsthat provide a more excellent signal feature than the cell of the basestation accessed by the UE. This process is distinguished from theinitial cell selection as Process No. 2 to be cell re-selection. In thiscase, a temporal constraint is given in order to prevent the cell frombeing frequently reselected with the variation of the signal feature. Acell selection procedure will be described below in detail.

FIG. 5 is a flowchart illustrating a process of establishing an RRCconnection.

The UE sends to the network an RRC connection request message forrequesting the RRC connection (S510). The network sends an RRCconnection setup message as a response to the RRC connection request(S520). The UE enters an RRC connection mode after receiving the RRCconnection setup message.

The UE sends to the network an RRC connection setup complete messageused to verify successful completion of establishing the RRC connection(S530).

FIG. 6 is a flowchart illustrating a process of reconfiguring the RRCconnection. The RRC connection reconfiguration is used to modify the RRCconnection. The RRC connection reconfiguration is used for perform RBestablishment/modification/release, handover, and measurementsetup/modification/release.

The network sends to the UE an RRC connection setup message formodifying the RRC connection (S610). The UE sends to the network an RRCconnection reconfiguration complete message used to verify successfulcompletion of establishing the RRC connection reconfiguration as aresponse to the RRC connection reconfiguration (S620).

Hereinafter, a radio link failure will be described.

The UE performs continuously performs measurement for the quality of aradio link with the serving cell that receives the service. The UEdecides whether communication is impossible under a current situationdue to deterioration in quality of the radio link with the serving cell.When the communication is almost impossible due to too low quality ofthe serving cell, the UE decides the current situation as a wirelessconnection failure.

When a radio link failure is decided, the UE abandons maintainingcommunication with a current serving cell, selects a new cell throughthe cell selection (alternatively, cell reselection) procedure, andattempts RRC connection re-establishment to a new cell.

FIG. 7 is an exemplary diagram illustrating a radio link failure. Anoperation associated with the radio link failure may be described as twophases.

In a first phase, the UE is in a normal operation and checks whetherthere is a problem in a current communication link. When the problem isdetected, the UE declares a radio link problem and waits for recovery ofthe radio link for a first stand-by time T1. When the radio link isrecovered until the first stand-by time elapses, the UE performs thenormal operation again. When the radio link is not recovered until thefirst stand-by time is expired, the UE declares the radio link failureand the UE enters a second phase.

In the second phase, the UE waits for recovering the radio link for thesecond stand-by time T2. When the radio is not recovered until thesecond stand-by time is expired, the UE enters the RRC idle state.Alternatively, the UE may perform the RRC re-establishment procedure.

The RRC connection re-establishment procedure is a procedure ofre-establishing the RRC connection again in the RRC_CONNECTED state.Since the UE stays in the RRC_CONNECTED state, that is, since the UEdoes not enter the RRC_IDLE state, the UE does not initialize all ofradio configurations (e.g., radio bearer configurations) thereof.Instead, when the UE starts the RRC connection reconfigurationprocedure, the UE temporarily suspends using all of the radio bearersexcept for SRBO. When the RRC connection reconfiguration is succeeded,the UE resumes using the radio bearers of which the use is temporarilysuspended.

FIG. 8 is a flowchart illustrating a success in a process ofreestablishing a connection.

The UE selects a cell by performing the cell selection. The UE receivesthe system information in order to receive basic parameters foraccessing the cell in the selected cell. In addition, the UE sends tothe base station the RRC connection reestablishment request message(S810).

When the selected cell is a cell having a context of the UE, that is, aprepared cell, the base station permits the RRC connectionreestablishment request of the UE and sends to the UE the RRC connectionreestablishment message (S820). The UE sends to the base station the RRCconnection reestablishment complete message to succeed in the RRCconnection re-establishment procedure (S830).

FIG. 9 is a flowchart illustrating a failure in the process ofreestablishing the connection. The UE sends to the base station the RRCconnection reestablishment request message (S810). When the selectedcell is not the prepared cell, the base station sends an RRC connectionre-establishment reject message to the UE as a response to the RRCconnection reestablishment request (S815).

Next, a procedure in which the UE selects the cell will be described indetail.

When the power of the UE is turned on or the UE stays in the cell, theUE performs procedures for receiving the service byselecting/reselecting a cell having appropriate quality.

The UE in the RRC idle state needs to prepare for receiving the servicethrough the cell by continuously selecting the cell having theappropriate quality. For example, the UE of which the power is justturned on needs to select the cell having the appropriate quality forregistration in the network. When the UE in the RRC connection stateenters the RRC idle state, the UE needs to select a cell to stay in theRRC idle state. As such, a process in which the UE selects a cell thatsatisfies a predetermined condition in order to stay in a servicestand-by state such as the RRC idle state is referred to as the cellselection. Since the UE performs the cell selection while the cell inthe RRC idle state may not be decided at present, it is important toselect the cell rapidly as possible. Therefore, in the case of a cellthat provides radio signal quality having a predetermined reference ormore, even though the cell is not a cell that provides the best radiosignal quality for the UE, the cell may be selected in the cellselection process by the UE.

Hereinafter, a method and a procedure for selecting the cell by the UEin the 3GPP LTE will be described in detail with reference to 3GPP TS36.304 V8.5.0 (2009-03) “User Equipment (UE) procedures in idle mode(Release 8)”.

When the power of the UE is turned on at an initial stage, the UEretrieves the public land mobile network (PLMN) and selects anappropriate PLMN capable of receiving the service. The PLMN is a networkthat is deployed or operated by a mobile network operator. Each mobilenetwork operator operates one or more PLMNs. The respective PLMNs may beidentified by a mobile country code (MCC) and a mobile network code(MNC). PLMN information of the cell is included in the systeminformation and broadcasted. The UE attempts to register the selectedPLMN. When the registration is succeeded, the selected PLMN becomes aregistered PLMN (RPLMN). The network may signal a PLMN list to the UEand the PLMNs included in the PLMN list may be considered as the PLMNsuch as the RPLMN. The UE registered in the network needs to bereachable by the network. When the UE is in the ECM-CONNECTED state(similarly, the RRC connection state), the network recognizes that theUE receives the service). However, when the UE is in the ECM-IDLE state(similarly, the RRC idle state), a situation of the UE is not effectivein the eNB, but the situation is stored in the MME. In this case, theposition of the UE which is in the ECM-IDLE state is known to only theMME as granularity of a list of tracking areas (TAs). A single TA isidentified by a tracking area identity configured by the PLMN identityto which the TA belongs and the tracking area code (TAC) uniquelyexpressing the TA in the PLMN.

Subsequently, the UE selects a cell having signal quality and feature toreceive an appropriate service among cells provided by the selectedPLMN.

The cell selection process is generally divided into two types.

First, as an initial cell selection process, the UE has no advanceinformation on the radio channel during this process. Therefore, the UEretrieves all radio channels in order to find the appropriate cell. TheUE finds the strongest cell in each channel. Thereafter, the UE selectsthe corresponding cell only at the time of finding the suitable cellthat satisfies the cell selection criterion.

Next, the UE may select the cell by using stored information or usinginformation broadcasted in the cell. Therefore, the cell selection maybe rapidly performed as compared with the initial cell selectionprocess. When the UE only finds the cell that satisfies the cellselection criterion, the UE selects the corresponding cell. When the UEdoes not find the suitable cell that satisfies the cell selectioncriterion through such a process, the UE performs the initial cellselection process.

After the UE selects a predetermined cell through the cell selectionprocess, the strength or quality of the signal between the UE and thebase station may be changed due to the mobility of the UE or a change ofa wireless environment. Therefore, when the quality of the selected celldeteriorates, the UE may select another that provides higher quality.When the cell is again selected as such, a cell that provides highersignal quality than the currently selected cell is generally selected.The process is referred to as the cell reselection. The cell reselectionprocess generally has a basic object o select the cell having thehighest quality to the UE.

In addition to the quality of the radio signal, the network decides apriority for each frequency to notify the priority to the UE. The UEthat receives the priority preferentially considers the priority to aradio signal quality criterion during the cell reselection process.

There may be a method for selecting or reselecting the cell according tothe signal feature of the wireless environment and there may be a cellreselection method described below according to the features of the RATand the frequency of the cell.

-   -   Intra-frequency cell reselection: The UE reselect a cell having        the same RAT and the same center-frequency as a cell which is        being camping.    -   Inter-frequency cell reselection: The UE reselects a cell having        the same RAT and a different center-frequency as the cell which        is being camping.    -   Inter-RAT cell reselection: The UE reselect a cell using an RAT        different from an RAT which is being camping.

A principle of the cell reselection process will be described below.

First, the UE measures the qualities of the serving cell and theneighboring cell for the cell reselection.

Second, the reselection is performed based on the cell reselectioncriterion. The cell reselection criterion has features described belowin association with the measurement of the serving cell and theneighboring cell.

The intra-frequency cell reselection is basically based on ranking. Theranking defines an index value for evaluating the cell reselection andthe cells are ordered in the order of the index value by using the indexvalue. A cell having the best index is generally called a best rankedcell. The cell index value is based on a value which the UE measures forthe corresponding cell and is applied with a frequency offset or a celloffset as necessary.

The inter-frequency cell reselection is based on a frequency priorityprovided by the network. The UE attempts to camp on a frequency havingthe highest frequency priority. The network may provide the frequencypriority to which in-cell UEs will commonly apply through broadcastsignaling or provide a frequency-dedicated priority for each UE throughUE-dedicated signaling.

The network may provide a parameter (e.g., a frequency-specific offset)used for the cell reselection to the UE for the inter-frequency cellreselection for each frequency.

The network may provide a neighboring cell list (NCL) used for the cellreselection to the UE for the intra-frequency cell reselection or theinter-frequency cell reselection. The NCL includes a cell-specificparameter (e.g., cell-specific offset) used in the cell reselection.

The network may provide a cell reselection black list used for the cellreselection to the UE for the intra-frequency cell reselection or theinter-frequency cell reselection. The UE does not perform the cellreselection for a cell included in the black list.

Subsequently, the ranking performed during the cell reselectionevaluating process will be described.

A ranking criterion used to give the priority of the cell is defined asillustrated in Equation 1.R _(S) =Q _(meas,s) +Q _(hyst) ,R _(n) =Q _(meas,n) −Q_(offset)  [Equation 1]

Herein, Rs represents a ranking criterion of the serving cell, Rnrepresents a ranking criterion of the neighboring cell, Qmeas,srepresents a quality value which the UE measures for the serving cell,Qmeas,n represents a quality value which the UE measures for aneighboring cell, Qhyst represents a hysteresis value for the ranking,and Qoffset represents an offset between two cells.

In an intra-frequency, when the UE receives an offset Qoffsets,n betweenthe serving cell and the neighboring cell, Qffoset=Qoffsets,n and whenthe UE does not receive Qoffsets,n, Qoffset=0.

In an inter-frequency, when the UE receives the offset Qoffsets,n firthe corresponding cell, Qoffset=Qoffsets,n+Qfrequency and when the UEdoes not receive Qoffsets,n, Qoffset=Qfrequency.

When the ranking varies while the ranking criterion Rs of the servingcell and the ranking criterion of the neighboring cell Rn are similar toeach other, the ranking is frequently reversed, and as a result, the UEmay alternatively reselect both cells. Qhyst represents a parameter forpreventing the UE from alternatively reselecting both cells by givinghysteresis in cell reselection.

The UE measures the Rs of the serving cell and the Rn of the neighboringcell according to the above equation and regards a cell having thelargest ranking criterion value as the best ranked cell and reselectsthis cell.

According to the criterion, it can be seen that the quality of the cellacts as the most important criterion in the cell reselection. If thereselected cell is not the suitable cell, the UE excludes thecorresponding frequency or the corresponding cell from a cell reselection target.

Hereinafter, a measurement and a measurement report will be described.

Supporting the mobility of the UE is required in the mobilecommunication system. Therefore, the UE continuously measures a qualityfor a serving cell that provides the service at present and a qualityfor a neighboring cell. The UE reports a measurement result to thenetwork at an appropriate time and the network provides optimal mobilityto the UE through handover. A measurement for the object is often calleda radio resource management (RPM) measurement.

The UE may perform a measurement having a specific object set by thenetwork and report a result of the measurement to the network in orderto provide information that may help an operator to operate the networkin addition to the object of supporting the mobility. For example, theUE receives broadcast information of a specific cell decided by thenetwork. The UE may report a cell identity (also referred to as a globalcell identity) of the specific cell, identification information (forexample, tracking area code) to which the specific cell belongs, and/orother cell information (for example, whether the specific cell is amember of the closed subscriber group (CSG) cell) to the serving cell.

When the UE which is moving verifies that a quality of a specific regionis too bad through the measurement, positional information on cellshaving a bad quality and a measurement result may be reported to thenetwork. The network may attempt optimization of the network based onreporting of measurement results of UEs that help operating the network.

In the mobile communication system in which a frequency reuse factor is1, mobility is generally made among different cells in the samefrequency band. Therefore, in order to well assure the mobility of theUE, the UE may well measure the qualities and cell information of theneighboring cells having the same center-frequency as the serving cell.A measurement for a cell having the same center-frequency as the servingcell as such is called an intra-frequency measurement. The UE reports ameasurement result to the network at an appropriate time by performingthe intra-frequency measurement to achieve an object of thecorresponding measurement result.

The mobile communication operator may operate the network by using aplurality of frequency bands. When the service of the communicationsystem is provided through the plurality of frequency bands, the UEneeds to be able to measure the qualities and cell information of theneighboring cells having a different center-frequency from the servingcell for assuring the optimized mobility for the UE. A measurement for acell having the different center-frequency as the serving cell as suchis called an inter-frequency measurement. The UE needs to be able toreport a measurement result to the network at an appropriate time byperforming the inter-frequency measurement.

When the UE supports a measurement for heterogeneous networks, the UEmay perform a measurement for cells of the heterogeneous networks by abase station configuration. The measurement for the heterogeneousnetworks is called an inter-radio access technology (RAT) measurement.For example, the RAT may include a UMTS terrestrial radio access network(UTRAN) and a GSM edge radio access network (GERAN) that follows a 3GPPstandard specification, and may include even a CDMA 2000 system thatfollows a 3GPP2 standard specification.

FIG. 10 is a flowchart illustrating the existing measurement performingmethod.

The UE receives measurement configuration information from the basestation (S1010). A message including the measurement configurationinformation is referred to as a measurement configuration message. TheUE performs a measurement based on the measurement configurationinformation (S1020). When a measurement result satisfies a reportingcondition in the measurement configuration information, the UE reportsthe measurement result to the base station (S1030). A message includingthe measurement result is referred to as a measurement report message.

The measurement configuration information may include informationdescribed below.

(1) Measurement object information: Represents information on an objectfor which the UE will perform the measurement. A measurement objectincludes at least one among an intra-frequency measurement object whichis an object of an intra-measurement, an inter-frequency measurementobject which is an object of an inter-measurement, and an inter-RATmeasurement object which is an object of an inter-RAT measurement. Forexample, the intra-frequency measurement object may indicate aneighboring cell having the same frequency band as the serving cell, theinter-frequency measurement object may indicate a neighboring cellhaving a different frequency band from the serving cell, and theinter-RAT measurement object may indicate a neighboring cell havingdifferent RAT from the serving cell.

(2) Reporting configuration information: Represents information on areporting condition and a report type regarding when the UE reports themeasurement result. The reporting condition may include information onan event or a cycle that triggers reporting the measurement result. Thereport type represents information regarding in which type themeasurement result is configured.

(3) Measurement identity information: Represents information on ameasurement identity to decide which measurement object, at a time when,and in which type the UE reports by associating the measurement objectwith the report configuration. The measurement identity information isincluded in the measurement report message, and as a result, it can beseen that for which measurement object the measurement result is andunder which reporting condition the measurement report occurs.

(4) Quantity configuration information: Represents information on aparameter for configuring filtering a measurement unit, a report unit,and/or a measurement result value.

(5) Measurement gap information: Represents information on a measurementgap which is an interval which the UE may use for only a measurementwithout considering data transmission with the serving cell becausedownlink transmission or uplink transmission is not scheduled.

The UE has a measurement object list, a measurement report configurationlist, and a measurement identity list in order to perform a measurementprocedure.

In the 3GPP LTE, the base station may configure only one measurementobject for one frequency band to the UE. According to Phrase 5.5.4 of3GPP TS 36.331 V8.5.0 (2009-03) “Evolved Universal Terrestrial RadioAccess (E-UTRA) Radio Resource Control (RRC); Protocol specification(Release 8)”, events that trigger a measurement report illustrated in atable described below are defined.

TABLE 1 Events Reporting conditions Event A1 Serving becomes better thanthreshold Event A2 Serving becomes worse than threshold Event A3Neighbour becomes offset better than serving Event A4 Neighbour becomesbetter than threshold Event A5 Serving becomes worse than threshold1 andneighbour becomes better than threshold2 Event B1 Inter RAT neighbourbecomes better than threshold Event B2 Serving becomes worse thanthreshold1 and inter RAT neighbour becomes better than threshold2

When the measurement result by the UE satisfies the configured event,the UE transmits the measurement report message to the base station.

FIG. 11 illustrates one example of a measurement configurationconfigured for the UE.

First, a measurement identity 1 1101 connects an intra-frequencymeasurement object and a report configuration 1 to each other. The UEperforms an intra frequency measurement and the report configuration 1is used to decide a criterion and a type of reporting a measurementresult.

A measurement identity 2 1102 is connected with the intra-frequencymeasurement object similarly as the measurement identity 1 1101, butconnects the intra-frequency measurement object to a reportconfiguration 2. The UE performs the intra frequency measurement and thereport configuration 2 is used to decide the criterion and the type ofreporting the measurement result.

The UE transmits the measurement result even though the measurementresult for the intra-frequency measurement object satisfies any one ofthe report configuration 1 and the report configuration 2, by themeasurement identity 1 1101 and the measurement identity 2 1102.

A measurement identity 3 1103 connects an inter-frequency measurementobject 1 and a report configuration 3 to each other. When a measurementresult for the inter-frequency measurement object 1 satisfies thereporting condition included in the report configuration 3, the UEreports the measurement result.

A measurement identity 4 1104 connects an inter-frequency measurementobject 2 and the report configuration 2 to each other. When ameasurement result for the inter-frequency measurement object 2satisfies the reporting condition included in the report configuration2, the UE reports the measurement result.

Meanwhile, the measurement object, the report configuration, and/or themeasurement identity may be added, changed, and/or deleted. Theaddition, the change, and/or the deletion may be instructed by sending anew measurement configuration message or sending a measurementconfiguration change message to the UE.

FIG. 12 illustrates an example of deleting a measurement identity. Whenthe measurement identity 2 1202 is deleted, a measurement for ameasurement object associated with the measurement identity 2 1202 isstopped and a measurement report is not also transmitted. Themeasurement object or the report configuration associated with thedeleted measurement identity may not be changed.

FIG. 13 illustrates an example of deleting a measurement object. Whenthe inter-frequency measurement object 1 is deleted, the UE also deletesthe associated measurement identity 3 1303. The measurement for theinter-frequency measurement object 1 is stopped and the measurementreport is not also transmitted. However, the report configurationassociated with the deleted first inter-frequency measurement object maynot be changed or deleted.

When the report configuration is removed, the UE removes even theassociated measurement identity. The UE stops measuring the associatedmeasurement object by the associated measurement identity. However, themeasurement object associated with the deleted report configuration maynot be changed or deleted.

The measurement report may include the measurement identity, a measuredquality of the serving cell, and a measurement result of the neighboringcell. The measurement identity identifies a measurement object in whichthe measurement report is triggered. The measurement result of theneighboring cell may include a cell identity and a measured quality ofthe neighboring cell. The measured quality may include at least one ofreference signal received power (RSRP) and reference signal receivedquality (RSRQ).

Subsequently, H(e)NB will be described.

The mobile communication service may be provided through a person, aspecific operator, or a base station possessed by a group in addition tothe mobile communication network operator. The base station is calledHome NB (HNB) or Home eNB (HeNB). Hereinafter, both the HNB and HeNB arecollectively the HeNB. The HeNB aims at basically providing a servicespecialized to only a closed subscriber group (CSG). However, theservice may be provided to users other than the CSG according to aconfiguration of an operating mode of the HeNB.

FIG. 14 is a diagram illustrating one example of a wirelesscommunication system illustrating a HeNB operation.

Referring to FIG. 14, a Home eNB gateway (HeNB GW) may be operated inorder to service the HeNB as such. The HeNBs is connected to the EPCthrough the HeNB GW or connected directly to the EPC. The HeNB GW isseen as a general eNB for the MME. The HeNB GW is seen as the MME forthe HeNB. Therefore, the HeNB and the HeNB GW are connected to eachother through an S1 interface and the HeNB GW and the EPC are alsoconnected to each other through the S1 interface. Further, even when theHeNB and the EPC are directly connected to each other, the HeNB and theEPC are connected to each other through the S1 interface. Most functionsof the HeNB are similar to those of a general eNB.

In general, the HeNB is lower than an eNB possessed by the mobilecommunication operator in radio transmission output. Therefore, servicecoverage provided by the HeNB is generally smaller than that provided bythe eNB. Due to such a feature, a cell provided by the HeNB is oftenclassified as a femto cell as compared with a macro cell provided by theeNB in terms of the service coverage. Meanwhile, in terms of theprovided service, when the HeNB provides the service to only the CSG,the cell provided by the HeNB is called a CSG cell.

Each CSG has its own unique identification number and the identificationnumber is called a CSG identity (ID). The UE may have a list of the CSGto which the UE belongs as a member and the CSG list may be changed by arequest from the UE or a command of the network. In general, one HeNBmay support one CSG.

The HeNB transfers a CSG ID of a CSG supported thereby through thesystem information to be accessed by only the member UE of thecorresponding CSG. When the UE discovers the CSG cell, the UE may verifywhich CSG the CSG cell supports by reading the CSG ID included in thesystem information. The UE that reads the CSG ID regards thecorresponding cell as a cell capable of access only when the UE itselfis a member of the corresponding CSG cell.

Even the HeNB need not permit only the CSG UE to access itself. The HeNBmay also permit a UE which is not the CSG member to access itselfaccording to a configuration of the HeNB. Which UE the HeNB permits toaccess itself depends on the configuration of the HeNB and herein, theconfiguration means a configuration of an operating mode of the HeNB.The operating mode of the HeNB is divided into three types describedbelow by considering which UE the HeNB provides the service to.

Closed access mode: Represents a mode to provide the service to aspecific CSG member. The HeNB provides the CSG cell.

Open access mode: Represents a mode to provide the service without alimitation of the specific CSG member like a general eNB. The HeNBprovides not the CSG cell but the general cell.

Hybrid access mode: Represents a mode to provide a CSG service to thespecific CSG member and provide the service to even a non-CSG memberlike the general cell. Recognized as the CSG cell by the CSG member UEand recognized as the general cell by the non-CSG member UE. Such a cellis called a hybrid cell.

The HeNB notifies whether a cell serviced thereby is the CSG cell or thegeneral cell to the UE to allow the UE to know whether the UE may accessthe corresponding cell. The HeNB operated in the closed access modebroadcasts that the HeNB itself is the CSG cell through the systeminformation. The HeNB operated in the open access mode broadcasts thatthe HeNB itself is not the CSG cell through the system information. Assuch, the HeNB encapsulates a 1-bit CSG indicator indicating whether thecell serviced thereby is the CSG cell in the system information. Forexample, the HeNB broadcasts that the serviced cell is the CSG cell bysetting the CSG indicator as TRUE. If the serviced cell is not the CSGcell, the CSG indicator may be set as FALSE or a method that skipstransmitting the CSG indicator may be used. Since the UE needs to beable to distinguish the general cell provided by the eNB from the CSGcell, the general eNB also transmit the CSG indicator to allow the UE toknow that the cell type provided thereby is the general cell. Thegeneral eNB does not transmit the CSG indicator to allow the UE to knowthat the cell type provided thereby is the general cell. Table 2illustrates a CSG associated parameter transmitted in a correspondingcell for each cell type. Subsequently, Table 3 illustrates a type of aUE that permits the access for each cell type.

TABLE 2 CSG cell General cell CSG indicator Indicating ‘CSG cell’Indicating ‘Non-CSG cell’ or not transmitted CSG identity Transmittingsupported Not transmitted CSG identity

TABLE 3 CSG cell General cell UE not supporting CSG InaccessibleAccessible Non-CSG member UE Inaccessible Accessible Member CSG UEAccessible Accessible

Hereinafter, inter-cell interference coordination (ICIC) will bedescribed.

The ICIC is a task that operates a radio resource so that a control ofinter-cell interference is maintained. An ICIC mechanism may be dividedinto frequency-domain ICIC and time-domain ICIC. The ICIC has amulti-cell radio resource management (RRM) function to requireconsidering information from multiple cells.

An interfering cell is a cell that provides interference. Theinterfering cell is also referred as an aggressor cell.

An interfered cell is a cell that is interfered by the interfering cell.The interfered cell is also referred to as a victim cell.

The frequency-domain ICIC coordinates the use of a frequency-domainresource (e.g., a resource block (RB)) among the multiple cells.

The time-domain ICIC coordinates a time-domain resource (e.g., asubframe) among the multiple cells. An operations, administration, andmaintenance (OAM) configuration called an almost blank subframe (ABS)pattern may be used for the time-domain ICIC. An ABS in the interferingcell is used to protect a resource in the subframe in the interferedcell that receives interference among strong cells. The ABS is asubframe that has reduced transmission power (alternatively, zerotransmission power) on the physical channel or has reduced activity.

A pattern based on the ABS is notified to the UE and restricts a UEmeasurement. This restriction is referred to as a measurement resourcerestriction. The ABS pattern represents information indicating whichsubframe is the ABS in one or more radio frames.

There are provided three measurement resource restriction patternsaccording to a measured cell (e.g., a serving cell or a neighbor cell)and measurement types (e.g., a radio resource management (RRM), a radiolink measurement (RLM), and channel state information (CSI)).

‘ABS pattern 1’ is used in an RRM/RLM measurement resource restrictionof the serving cell. The base station may notify information on ABSpattern 1 to the UE in configuration/modification/release of the RB orwhen MAC/PHY configuration is modified.

‘ABS pattern 2’ is used in an RRM measurement resource restriction ofthe neighbor cell that operates at the same frequency as the servingcell. Therefore, a list of neighbor cells to be measured in addition toinformation on ABS pattern 2 may be provided to the UE. ABS pattern 2may be included in a measurement configuration for a measurement object.

‘ABS pattern 3’ is used in a resource restriction for a CSI measurementof the serving cell. ABS pattern 3 may be included in a message forconfiguring a CSI report.

Two scenarios of a CSG scenario and a pico scenario are considered forthe ICIC.

FIG. 15 exemplifies a CSG scenario.

The CSG cell represents a cell accessible by only a specific subscriber.The non-member UE as a UE which is not the member of the CSG cell is UEthat does not access the CSG cell. The CSG cell which the UE may notaccess is referred to as the non-member CSG cell. The macro cellrepresents the serving cell of the non-member UE. Coverage of the CSGcell and coverage of the macro cell are partially or fully duplicatedwith each other.

A primary interference condition occurs when the non-member UE ispositioned in close proximity with the CSG cell. In terms of thenon-member UE, the interfering cell becomes the CSG cell and the macrocell becomes the interfered cell. The time-domain ICIC is used so as forthe non-member UE to continuously receive the service in the macro cell.

In the RRC connection state, when the network discovers that thenon-member UE belongs to strong interference from the CSG cell, thenetwork may configure a measurement resource restriction. Further, inorder to facilitate mobility from the macro cell, the network mayconfigure an RRM measurement resource restriction for the neighbor cell.When the UE is not strongly interfered from the CSG cell any longer, thenetwork may release the RRM/RLM/CSI measurement resource restriction.

The UE may use the measurement resource restrictions configured for theRRM, RLM, and CSI measurement. That is, a resource for the RLM may beused in the ABS, and the measurement for the RLM and the CSI measurementmay be performed in the ABS.

The network may configure the CSG cell not to use a low-interferenceradio resource depending on the configured measurement resourcerestriction. That is, the CSG cell may not transmit or receive data inthe ABS.

FIG. 16 exemplifies a pico scenario.

A pico cell is a serving cell of a pico UE. The pico cell is a cell ofwhich coverage is partially or fully duplicated with the coverage of themacro cell. The pico cell may generally have smaller coverage than themacro cell, but the present invention is not particularly limitedthereto.

The primary interference condition occurs when the pico UE is positionedat an edge of the pico serving cell. In terms of the pico UE, theinterfering cell becomes the macro cell and the pico cell becomes theinterfered cell. The time-domain ICIC is used so as for the pico UE tocontinuously receive the service in the pico cell.

When the pico cell discovers that the pico UE is strongly interferedfrom the macro cell, the pico cell may configure the measurementresource restriction for the corresponding UE.

The pico UE may use the measurement resource restrictions configured forthe RRM, RLM, and CSI measurement. That is, the resource for the RLM maybe used in the ABS, and the measurement for the RLM and the CSImeasurement may be performed in the ABS. When the pico cell is stronglyinterfered from the macro cell, a more accurate measurement is possiblein the case where the RRM/RLM/CSI measurement is performed in the ABS.

Further, when the UE in the macro cell as the serving cell performs themeasurement for the neighbor cell in the ABS, mobility from the macrocell to the pico cell may be facilitated.

The UE performs the RRM measurement such as the reference signalreceived power (RSRP) and the reference signal received quality (RSRQ),a measurement of quality such as a channel quality indicator (CQI), anda path-loss measurement for the serving cell or the neighbor cell.Further, the UE may perform a measurement for radio link monitoring(RLM) for monitoring a connection with the serving cell.

The interfering cell and the interfered cell are decided depending on anobject which the UE intends to measure.

When the UE intends to measure the serving cell, an intra-frequencyneighbor cell having a high signal strength near the UE may act asinterference in a measurement for the serving cell. In this case, the UEmay undergo strong interference by the neighbor cell in the measurementfor the serving cell.

When the UE intends to measure the intra-frequency neighbor cell,serving cell and other intra-frequency neighbor cell signals may act asthe interference for the measurement of the intra-frequency neighborcell. In this case, the UE may undergo strong interference by theserving cell and other neighbor cells of a serving frequency in themeasurement of the neighbor cell.

When the serving cell may know information on a measurement resourcerestriction which the neighbor cell causing the UE to be interferedapplies for suppressing the interference, the interfered UE may performa limited measurement based on the measurement resource restriction. Theserving cell may provide the service the UE through scheduling primarilyusing a low-interference radio resource in spite of the interference bythe neighbor cell.

A multimedia broadcast/multicast service (MBMS) is a service to providemultimedia data to the UE in the cell. An MCH channel which is atransmission channel for the MBMS may be mapped to the MCCH or the MTCHwhich is the logical channel. The MCCH transmits an RRC messageassociated with the MBMS and the MTCH transmits traffic of a specificMBMS.

A plurality of MCHs may be used according to capacities of the MTCH andthe MCCH in one cell. The MCH is in charge of transmitting two logicalchannels of the MTCH and the MCCH, and is again mapped to a physicalmulticast channel (PMCH) which is the physical channel.

One MCCH is present in one MBMS single frequency network (MBSFN) regiontransmitting the same MBMS information/traffic, and when a plurality ofMBSFN regions are provided in one cell, the UE may receive a pluralityof MCCHs. When the MBMS associated RRC message is changed in a specificMCCH channel, the PDCCH transmits an MBMS radio network temporaryidentity (M_RNTI) and an indicator indicating the specific MCCH.

A UE that supports the MBMS receives the M-RNTI and the MCCH indicatorthrough the PDCCH to determine that the MBMS associated RRC message ischanged in the specific MCCH and receive the specific MCCH. The RRCmessage of the MCCH may be changed every change cycle and is repeatedlybroadcasted every repetition cycle.

The existing wireless network may calculate the number of UEs thatreceives a specific service through a counting procedure. The countingprocedure is configured in such a manner that the UE transmits an uplinkcounting response message when the wireless network transmits a downlinkcounting request message.

When UE is requested to report system information about a neighboringcell from a serving cell, the UE temporarily leaves the serving cell,accesses the neighboring cell, and obtains the system information aboutthe neighboring cell. Thereafter, the UE accesses the serving cell againand performs a procedure for reporting information about the neighboringcell to the serving cell. While the UE leaves the serving cell in orderto obtain the system information, the serving cell is unable to transferany command/message/data to the UE because the UE corresponds to anunreachable object from a viewpoint of the serving cell.

If UE has had ready-acquired system information about a correspondingneighboring cell before receiving a system information report requestand the ready-acquired system information is valid system informationthat can be reported to a serving cell, an operation of the UE receivingthe system information report request and leaving to newly acquire thesystem information about the corresponding neighboring cell correspondsto an unnecessary operation.

Accordingly, there is proposed a method in which when a serving cellrecognizes that UE has had ready-acquired system information about aneighboring cell, the serving cell requests the UE to report thecorresponding system information and the UE reports the ready-acquiredsystem information to the serving cell in response thereto. Furthermore,there is proposed a mechanism in which UE notifies a serving cell thatthe UE has had ready-acquired system information.

In accordance with an embodiment of the present invention, if UE has hadready-acquired system information about a neighboring cell, the UEnotifies a serving cell of such a state. The serving cell that has beenaware that the UE has the ready-acquired system information about theneighboring cell may instruct the UE to report the ready-acquired systeminformation instead of newly acquiring, by the UE, system informationabout the neighboring cell and transmitting the newly acquired systeminformation when the serving cell requests the UE to report systeminformation about the neighboring cell.

Furthermore, a serving cell may request UE to notify information aboutwhether or not the UE has ready-acquired system information about aneighboring cell. To this end, the serving cell may include aready-acquired system information notification request indicator in ameasurement configuration and transmit the ready-acquired systeminformation notification request indicator. The indicator may beincluded in the target measurement configuration and/or the measurementreport condition configuration of a measurement configuration.

When sending an uplink signaling message to a serving cell, UE maynotify the serving cell that it has stored ready-acquired systeminformation about a neighboring cell. For example, when UE reports aquality measurement result of a neighboring cell having a satisfiedmeasurement report condition, the UE may include an indicator,indicating that the UE has ready-acquired system information about theneighboring cell, in a measurement report and send the measurementreport.

A method of reporting system information in accordance with anembodiment of the present invention is described in detail below withreference to the drawings.

FIG. 17 is a flowchart illustrating a method of reporting systeminformation in accordance with an embodiment of the present invention.It is assumed that UE has acquired system information from a neighboringcell before a system information report request and has theready-acquired system information.

Referring to FIG. 17, a serving cell requests the UE to notify theserving cell whether or not the UE has the ready-acquired systeminformation about the neighboring cell (S1710). To this end, the servingcell may send a ready-acquired system information query indicator to theUE. The ready-acquired system information query indicator may beincluded in a measurement configuration and transmitted. The indicatormay be included in the target measurement configuration of a measurementconfiguration.

When the UE receives the ready-acquired system information queryindicator from the serving cell, the UE transmits a ready-acquiredsystem information availability indicator, indicating that the UE hasthe ready-acquired system information about the neighboring cell, to theserving cell (S1720) in response to the ready-acquired systeminformation query indicator. The ready-acquired system informationavailability indicator may be included in a measurement report that istransmitted from the UE to the serving cell in order to report ameasurement result when a measurement report condition on thecorresponding neighboring cell is satisfied and then transmitted.

When the ready-acquired system information availability indicator isreceived from the UE, the serving cell may determine whether to receivea report on the ready-acquired system information or whether to instructthe UE to newly acquire system information and report the newly acquiredsystem information. The serving cell that has not received theready-acquired system information availability indicator from the UE mayinstruct the UE to newly acquire system information and report the newlyobtained system information.

If the serving cell determines to receive a report on the ready-acquiredsystem information, the serving cell transmits a system informationreporting request, including a ready-acquired system informationreporting request indicator, to the UE (S 1730). In this case, theindicator can be configured to report the ready-acquired systeminformation.

In contrast, if the serving cell determines that the UE acquire systeminformation again from the neighboring cell and then reports thecorresponding system information, the serving cell may include theready-acquired system information reporting request indicator,configured to instruct the UE to acquire system information from theneighboring cell and report the acquired system information, in thesystem information reporting request and transmit the system informationreporting request or may transmit the system information reportingrequest not including the indicator to the UE.

When the UE receives the ready-acquired system information reportingrequest indicator that instructs the UE to report the ready-acquiredsystem information from the serving cell, the UE includes theready-acquired system information in a system information report andtransmits the system information report to the serving cell in responsethereto (S1740). An indicator indicating that the included systeminformation is the ready-acquired system information acquired by the UEfrom the neighboring cell prior to the system report request may beincluded in the system information report.

When UE receives a system information reporting request that includesthe ready-acquired system information reporting request indicatorconfigured to instruct the UE to acquire system information from aneighboring cell and report the obtained system information or that doesnot include the indicator from a serving cell, the UE accesses theneighboring cell and acquires the system information. After acquiringthe system information, the UE accesses the serving cell again andtransmits a system information report, including the acquired systeminformation, to the serving cell. An indicator indicating that theincluded system information is new system information acquired from theneighboring cell after the system information reporting request wasreceived may be included in the system information report.

Meanwhile, in sending the ready-acquired system information availabilityindicator to the serving cell, control information related to the systeminformation may also be transmitted to the serving cell. The controlinformation may include information about the ID of the neighboring cellthat is related to the system information, information related to apoint of time at which the system information was acquired and/orinformation about the type of ready-acquired system information.

The information about the type of ready-acquired system information maybe information about pieces of detailed information included in thesystem information. The information about the type of system informationcan be configured to indicate whether or not the pieces of detailedinformation are present or not.

If the control information, together with the indicator, is transmitted,the serving cell may determine whether to instruct the UE to report theready-acquired system information or whether to instruct the UE to newlyacquire system information from the neighboring cell and report thenewly acquired system information based on the control information. Forexample, if it is determined that availability duration of a specificvalue has elapsed from a point of time at which the ready-acquiredsystem information was acquired, the serving cell may request the UE tonewly acquire system information about the neighboring cell and reportthe newly acquired system information to the serving cell. For anotherexample, if the information about the type of ready-acquired systeminformation indicates that specific individual information that isdesired to be acquired by the serving cell is not included, the servingcell may request the UE to newly acquire system information about theneighboring cell and report the newly acquired system information to theserving cell.

In order to perform the method of reporting system information inaccordance with an embodiment of the present invention, UE may storespecific system information about a neighboring cell for a specific timeor more. When UE receives system information about a cell that isfrequently visited by a specific user, for example, a cell installed atthe house of the user or a cell installed at the company of the user,the UE may store the system information about the cell in order tosubsequently report the system information about the cell. In thepresent invention, if UE stores system information for the purpose ofreporting the system information, the UE may be allowed to store thesystem information for a time that exceeds the valid time of commonsystem information.

In the aforementioned embodiment of the method of reporting systeminformation, the system information that is reported from the UE to theserving cell may include pieces of the following detailed information.

If a cell related to system information is a cell supporting a CSG,reported system information may include CSG-related information aboutthe cell, such as a CSG ID or CSG indicator.

If a cell related to system information is a cell supporting MBMS,reported system information may include MBMS-related information aboutthe cell, such as MBMS service information, MBMS configurationinformation, MBMS scheduling information, frequency information aboutprovided MBMS service and/or MBSFN subframe information.

If a cell related to system information is a cell in which a measurementresource limit has been set, reported system information may include lowinterference radio resource-related information about the cell, such asABS pattern information, low interference subframe pattern information,or a limited measurement pattern.

The reported system information may include access limit-relatedinformation, such as an access class-barring parameter.

The reported system information may be information about one or moreuplink frequency bands associated with the downlink of a specific cell.

In the aforementioned embodiment of the present invention, when aserving cell requests that system information about a neighboring cellbe reported, the serving cell may transfer a system informationindicator, indicating that specific individual information belonging tothe system information about the neighboring cell should be reported, toUE. The system information indicator may be implemented so that a reporton corresponding information is requested in such a manner that onesystem information indicator indicates one or more types of information.The system information indicator may be implemented so that one or morespecific types of information are requested through the transmission ofone or more system information indicators in such a manner that oneindicator indicates a specific type of information.

The system information indicator may be included in a measurementconfiguration and transmitted and may be transmitted along with a systeminformation report request. The system information indicator may beincluded in a target measurement configuration and/or a measurementreport configuration. Specific information that is requested to bereported may be at least one of CSG-related information, MBMS-relatedinformation low interference radio resource-related information, accesslimit-related information, and information about one or more uplinkfrequency bands associated with the downlink of a specific cell.

In the aforementioned embodiment of the present invention, in reportingready-acquired system information and/or system information, newlyacquired after a system information reporting request, to a servingcell, UE may transmit the ready-acquired system information and/or thenewly acquired system information to the serving cell along withspecific information that has been determined/processed based on thecorresponding system information.

The specific information may include information indicating whether ornot UE is a member of a CSG regarding a corresponding neighboring cell.

The specific information may include information indicating whether ornot UE can access a corresponding neighboring cell.

The specific information may include information indicating whether ornot UE can be supplied with desired specific service from acorresponding neighboring cell. For example, the specific informationmay include information indicating whether or not the UE can be servedwith MBMS information from the cell.

The specific information may be information indicating whether or notspecific radio resources can be configured for UE in a correspondingneighboring cell. For example, the specific information may beinformation indicating whether or not UE can camp on in the cell. Thespecific information may be information indicating whether or not thecell is a cell suitable for UE. The specific information may beinformation indicating whether or not the cell is a cell that may beused by UE as a serving cell through a carrier aggregation or may besystem information necessary to configure the cell as a serving cellthrough a carrier aggregation.

The specific information may include information indicating whether ornot a corresponding neighboring cell is a cell that may be used by UE asan additional serving cell Pcell or Scell.

Through the method of reporting system information in accordance with anembodiment of the present invention, UE can effectively notify a servingcell that it has system information about a neighboring cell.Accordingly, a serving cell can request UE to report system informationabout a neighboring cell in an optimized manner. As a result, the timethat is consumed for a serving cell to acquire system information abouta neighboring cell can be reduced. If such a method of reporting systeminformation is applied to a mobility performing method of UE, such as ahandover, delay occurring when mobility is performed can be reduced andmobility can be performed more efficiently. This can lead to theimprovement of communication quality.

FIG. 18 is a block diagram showing a wireless device in which anembodiment of the present invention can be implemented. The device canimplement UE that performs and/or a BS of a serving cell or aneighboring cell which perform the system report method in accordancewith the embodiment of FIG. 17.

The wireless device 1800 includes a processor 1810, memory 1820, and aRadio Frequency (RF) unit 1830. The processor 1810 implements theproposed functions, processes and/or methods. The processor 1810 can beconfigured to report system information about a neighboring cell to aserving cell in response to a system information reporting request. Theprocessor 1810 can be configured to send a ready-acquired systeminformation query indicator that requests another wireless device toprovide notification of whether ready-acquired system information abouta neighboring cell is present or not. The processor 1810 can beconfigured to send a ready-acquired system information availabilityindicator in response to a ready-acquired system information queryindicator. The processor 1810 can be configured to determine whether ornot to report ready-acquired system information about a specificneighboring cell or whether or not to newly acquire system informationand report the newly acquired system information based on aready-acquired system information availability indicator received fromanother wireless device. The processor 1810 can be configured to requestthat system information be reported. The processor 1810 can beconfigured to report ready-acquired system information or to acquiresystem information from a specific neighboring cell and report theacquired system information to a serving cell. The processor 1810 can beconfigured to implement the method of reporting system information inaccordance with the aforementioned embodiment of FIG. 17.

The RF unit 1830 is connected to the processor 1810 and sends andreceives radio signals.

The processor 1810 may include Application-Specific Integrated Circuits(ASICs), other chipsets, logic circuits, and/or data processors. Thememory 1820 may include Read-Only Memory (ROM), Random Access Memory(RAM), flash memory, memory cards, storage media and/or other storagedevices. The RF unit 1830 may include baseband circuits for processingradio signals. When the embodiment is implemented in software, theaforementioned scheme may be implemented as a module (process orfunction) that performs the aforementioned function. The module may bestored in the memory 1820 and executed by the processor 1810. The memory1820 may be placed inside or outside the processor 1810 and may beconnected to the processor 1810 using a variety of well-known means.

In the above exemplary system, although the methods have been describedbased on the flowcharts in the form of a series of steps or blocks, thepresent invention is not limited to the sequence of the steps, and someof the steps may be performed in a different order from that of othersteps or may be performed simultaneous to other steps. Furthermore,those skilled in the art will understand that the steps shown in theflowchart are not exclusive and the steps may include additional stepsor that one or more steps in the flowchart may be deleted withoutaffecting the scope of the present invention.

What is claimed is:
 1. A method of reporting, by user equipment, systeminformation in a wireless communication system, the method comprising:transmitting a ready-acquired system information availability indicatornotifying a serving cell that ready-acquired system information about aneighboring cell is present, and control information about theready-acquired system information to the serving cell wherein thecontrol information comprises: information about an identifier of theneighboring cell related to the ready -acquired system information;indication information indicating a point of time at which the ready-acquired system information was acquired; and information indicating atype of ready-acquired system information; receiving a systeminformation reporting request from the serving cell; and sending asystem information report to the serving cell in response to the systemreporting request, wherein if the system reporting request comprises aready-acquired system information reporting request indicator and theready-acquired system information reporting request indicator indicatesthat the ready-acquired system information is to be reported, the systeminformation report comprises the ready-acquired system information,wherein the ready-acquired system information is system informationacquired from the neighboring cell before receiving the system reportingrequest; if the system reporting request comprises the ready-acquiredsystem information reporting request indicator and the ready-acquiredsystem information reporting request indicator indicates that the systeminformation is to be acquired from the neighboring cell and to bereported, acquiring new system information from the neighboring cell andreporting the newly acquired system information to the serving cell; andif the system reporting request does not include the ready-acquiredsystem information reporting request indicator, acquiring the new systeminformation from the neighboring cell and reporting the new acquiredsystem information to the serving cell.
 2. The method of claim 1,wherein the system information report further comprises an indicatorindicating whether system information included in the system informationreport is the ready-acquired system information or the newly acquiredsystem information.
 3. The method of claim 1, further comprisingreceiving a ready-acquired system information query indicator from theserving cell, the ready-acquired system information query indicatorrequesting to notify that whether the ready-acquired system informationis present, wherein the ready-acquired system information availabilityindicator is transmitted in response to the ready-acquired systeminformation query indicator.
 4. The method of claim 1, wherein: aready-acquired system information query indicator is included in ameasurement configuration message and transmitted, and theready-acquired system information availability indicator is included ina measurement report message and transmitted.
 5. A user equipmentoperating in a wireless communication system, the user equipmentcomprises: a Radio Frequency (RF) unit sending and receiving radiosignals; and a processor functionally connected to the RF unit, whereinthe processor is configured for: transmitting a ready-acquired systeminformation availability indicator notifying a serving cell thatready-acquired system information about a neighboring cell is present,and control information about the ready-acquired system information tothe serving cell wherein the control information comprises: informationabout an identifier of the neighboring cell related to theready-acquired system information; indication information indicating apoint of time at which the ready-acquired system information wasacquired; and information indicating a type of ready-acquired systeminformation; receiving a system information reporting request from theserving cell; and sending a system information report to the servingcell in response to the system reporting request, wherein if the systemreporting request comprises a ready-acquired system informationreporting request indicator and the ready-acquired system informationreporting request indicator indicates that the ready-acquired systeminformation is to be reported, the system information report comprisesthe ready-acquired system information, wherein the ready-acquired systeminformation is system information acquired from the neighboring cellbefore receiving the system reporting request; if the system reportingrequest comprises the ready-acquired system information reportingrequest indicator and the ready-acquired system information reportingrequest indicator indicates that the system information is to beacquired from the neighboring cell and to be reported, the processor isfurther configured for acquiring new system information from theneighboring cell and reporting the newly acquired system information tothe serving cell; and if the system reporting request does not includethe ready-acquired system information reporting request indicator, theprocessor is further configured for acquiring the new system informationfrom the neighboring cell and reporting the new acquired systeminformation to the serving cell.
 6. The user equipment of claim 5,wherein the system information report further comprises an indicatorindicating whether system information included in the system informationreport is the ready-acquired system information or the newly acquiredsystem information.
 7. The user equipment of claim 5, wherein theprocessor is further configured for receiving a ready-acquired systeminformation query indicator from the serving cell, the ready-acquiredsystem information query indicator requesting to notify that whether theready-acquired system information is present, and wherein theready-acquired system information availability indicator is transmittedin response to the ready-acquired system information query indicator. 8.The user equipment of claim 5, wherein: a ready-acquired systeminformation query indicator is included in a measurement configurationmessage and transmitted, and the ready-acquired system informationavailability indicator is included in a measurement report message andtransmitted.